1. Field of the Invention
The present invention relates to a non-volatile memory structure and a manufacturing method thereof, and more particularly, to a silicon-oxide-nitride-oxide-semiconductor (hereinafter abbreviated as SONOS) non-volatile memory structure and a manufacturing method thereof.
2. Description of the Prior Art
Semiconductor memory devices are prevalently used in computer and electronics industries as a means for retaining digital information. Typically, the semiconductor memory devices are divided into volatile and non-volatile memory devices depending on whether the data stored in the memory devices is completely lost or not in case of power interruption. And the non-volatile memory devices, which can retain their data even when the power supply is interrupted, have been widely employed.
In the conventional non-volatile memory technology, a SONOS memory structure is used to build a silicon nitride layer sandwiched between two silicon oxide layers for serving as the charge trap layer while the two silicon oxide layers respectively serve as a charge tunnel layer and a charge block layer. This oxide-nitride-oxide (ONO) multilayered structure is further formed between a semiconductor substrate and a silicon floating gate, and thus a SONOS memory structure is constructed.
Since the microprocessors have become more powerful, requirements of memory devices of large-capacity and low-cost are raised. To satisfy such trend and achieve challenge of high integration in semiconductor devices, memory miniaturization is kept on going, and thus fabrication process of memory structure is getting complicated. Furthermore, it is observed that the elements for constructing semiconductor devices are getting more and more susceptible to the process and thus the process control for ensuring yield and performance of the semiconductor devices becomes more and more important. For example, the nitride layer, which serves as the charge trapping layer, plays the essential role for storing data, therefore it is always important to protect the nitride layer in the fabrication process.